The present invention relates to an optical information recording and reproducing apparatus, and in particular to an optical information recording and reproducing apparatus which can be continuously and quickly changed over without lowering the recording density, in a mode for writing information onto an optical information recording disk (optical disk), between a read operation for reading address information (ID information) recorded beforehand on the optical disk and a write operation for writing information into a desired address.
In order to keep laser luminous power in a read operation at a constant value in conventional optical information recording and reproducing apparatuses (optical disk apparatuses), a part of laser light is received by a photodiode whose output is used for negative feedback control. If the negative feedback control is effected when information is to be written onto the optical disk, however, the average power of the laser light modulated by the recording information is controlled to be equal to the luminous power in a read operation. Thus the power level of the write laser is lowered, the write operation being disabled.
In one scheme of the prior art for solving the above described problem, the reference voltage compared with the output of a photodiode for monitoring the laser luminous power is switched to such a higher value in the write operation as compared with the read operation that the average power of laser light modulated by the recording information will become a desired luminous power as a result of negative feedback control. In another scheme as described in JP-A-59-79440 (laid open on May 8, 1984), a sample/hold circuit is disposed in the negative feedback control system to hold the voltage for providing the laser luminous power in read operation during the write period. As a result, the write pulse signal modulated by the information signal is added to the above described laser luminous power in the read operation.
In the former scheme (prior art 1), however, changeover between the write operation and the read operation cannot be made at high speed because of the slow response of the negative feedback control system. Accordingly information cannot be written continuously and rapidly. In the latter scheme (prior art 2), it is not considered to properly assure the low level of laser light modulated by the recording information. As will be apparent from the description below, therefore, the information sometimes cannot be written properly. In addition, the recording density of the optical disk must be unadvantageously lowered in order to avoid the state in which the ID information cannot be properly detected.